Giant Concrete Targets
Near Casa Grande, there are enormous cross-shaped targets that span 16 miles in each direction. You can see these strange structures through Google maps. While they might seem eerie, these are calibration targets leftover from the Cold War.
During the 1960s, the U.S. Army launched the Corona satellites. These targets were built to calibrate those satellites. Originally, there were 145 targets, all a mile apart from each other. Two of them have disappeared over the past 50 years.